diff --git a/lib/engine.rb b/lib/engine.rb
--- a/lib/engine.rb
+++ b/lib/engine.rb
@@ -1,5 +1,4 @@
 require 'fileutils'
-require 'ftools'
 require File.join(File.dirname(__FILE__),'dir_init')
 
 module Grader
@@ -139,7 +138,7 @@
         fname = File.basename(s)
         if !FileTest.exist?("#{script_dir}/#{fname}")
           copied << fname
-          system("cp #{s} #{script_dir}")
+          FileUtils.cp(s, "#{script_dir}")
         end
       end
       
@@ -174,7 +173,7 @@
 
     def clear_script(log,problem_home)
       log.each do |s|
-        system("rm #{problem_home}/script/#{s}")
+        FileUtils.rm("#{problem_home}/script/#{s}")
       end
     end
 
diff --git a/lib/test_request_helper.rb b/lib/test_request_helper.rb
--- a/lib/test_request_helper.rb
+++ b/lib/test_request_helper.rb
@@ -5,6 +5,23 @@
 
 module Grader
 
+  def self.link_or_copy(src, des)
+    begin
+      FileUtils.ln_s(src, des)
+    rescue
+      FileUtils.cp(src,des)
+    end
+  end
+
+  def self.call_and_log(error_message)
+    begin
+      yield
+    rescue
+      msg = "ERROR: #{error_message}"
+      raise msg
+    end
+  end
+   
   #
   # A TestRequestRoomMaker is a helper object for Engine
   # - finds grading room: in user_result_dir/(user)/test_request/ ...
@@ -28,8 +45,8 @@
       #    to the sandbox directory later.  The run script should do it.
       #
       if FileTest.exists?("#{test_request.input_file_name}.files")
-        cmd = "cp #{test_request.input_file_name}.files/* #{grading_room}"
-        system(cmd)
+        FileUtils.cp_r("#{test_request.input_file_name}.files/.",
+                       "#{grading_room}")
       end
 
       grading_room
@@ -82,11 +99,12 @@
     end
     
     def copy_problem_template(template_dir,problem_home)
-      cmd = "cp -R #{template_dir}/* #{problem_home}"
-      system_and_raise_when_fail(cmd,"Test Request: cannot copy problem template")
+      Grader::call_and_log("Test Request: cannot copy problem template") {
+        FileUtils.cp_r("#{template_dir}/.","#{problem_home}")
+      }
     end
-    
-    def link_input_file(test_request,problem_home)
+
+    def link_input_file(test_request, problem_home)
       input_fname = "#{test_request.input_file_name}"
       if !File.exists?(input_fname)
         raise "Test Request: input file not found."
@@ -97,20 +115,14 @@
         FileUtils.rm([input_fname_problem_home], :force => true)
       end
 
-      cmd = "ln -s #{input_fname} #{input_fname_problem_home}" 
-      system_and_raise_when_fail(cmd,"Test Request: cannot link input file")
+      Grader::link_or_copy("#{input_fname}", "#{input_fname_problem_home}")
     end
     
     def remove_data_files(problem_home)
       if File.exists?("#{problem_home}/test_cases/1/input-1.txt")
-        cmd = "rm #{problem_home}/test_cases/1/*"
-        system_and_raise_when_fail(cmd,"Test Request: cannot remove data files")
-      end
-    end
-    
-    def system_and_raise_when_fail(cmd,msg)
-      if !system(cmd)
-        raise msg
+        Grader::call_and_log("Test Request: cannot remove data files") {
+          FileUtils.rm Dir.glob("#{problem_home}/test_cases/1/*")
+        }
       end
     end
     
@@ -221,10 +233,7 @@
       target_file_name = random_output_file_name(test_request.user,
                                                  test_request.problem)
       FileUtils.mkdir_p(File.dirname(target_file_name))
-      cmd = "ln -s #{fname} #{target_file_name}"
-      if !system(cmd)
-        raise "TestRequestReporter: cannot move output file"
-      end
+      Grader::link_or_copy("#{fname}", "#{target_file_name}")
       return target_file_name
     end
 
diff --git a/std-script/judge b/std-script/judge
--- a/std-script/judge
+++ b/std-script/judge
@@ -1,5 +1,7 @@
 #!/usr/bin/ruby
 
+require 'fileutils'
+
 def log(str='')
   if ENV['TALKATIVE']!=nil
     puts str
@@ -22,6 +24,21 @@
   end
 end
 
+def call_and_log(error_message)
+  begin
+    yield
+  rescue
+    msg = "ERROR: #{error_message}"
+    log msg
+    raise msg
+  end
+end
+
+def clear_and_create_empty_dir(dir)
+  FileUtils.rm_rf(dir, :secure => true)
+  call_and_log("Cannot make directory #{dir}.") { FileUtils.mkdir(dir) }
+end
+
 # ARGV[0] --- language
 # ARGV[1] --- program source file
 # ARGV[2] --- test result directory
@@ -57,9 +74,9 @@
 else
   test_result_dir = "#{current_dir}/test-result"
 end
+
 log "Test result directory: #{test_result_dir}"
-system("rm -Rf #{test_result_dir}")
-execute("mkdir #{test_result_dir}", "Cannot make directory #{test_result_dir}.")
+clear_and_create_empty_dir(test_result_dir)
 
 if ARGV.length >= 4
   sandbox_dir = ARGV[3]
@@ -67,13 +84,14 @@
   sandbox_dir = "#{current_dir}/sandbox"
 end
 log "Sandbox directory: #{sandbox_dir}"
-system("rm -Rf #{sandbox_dir}")
-execute("mkdir #{sandbox_dir}", "Cannot make directory #{sandbox_dir}")
+clear_and_create_empty_dir(sandbox_dir)
 
 # Compile
 log
 log "Compiling..."
-execute("cp #{source_file} #{sandbox_dir}", "Cannot copy the source file to #{sandbox_dir}")
+call_and_log("Cannot copy the source file to #{sandbox_dir}") { 
+  FileUtils.cp(source_file, sandbox_dir) 
+}
 begin 
   Dir.chdir sandbox_dir
 rescue
@@ -83,13 +101,17 @@
 execute("#{problem_home}/script/compile #{language} #{source_file}", "Compilation error!")
 compile_message = `cat compiler_message`
 compile_message.strip!
-execute("mv compiler_message #{test_result_dir}", "Cannot move the compiler message to #{test_result_dir}.")
+call_and_log("Cannot move the compiler message to #{test_result_dir}.") {
+  FileUtils.mv("compiler_message", test_result_dir)
+}
 if !FileTest.exist?("a.out")
   log "Cannot compile the source code. See message in #{test_result_dir}/compile_message"
   exit(127)
 else
-  execute("mv a.out #{test_result_dir}", "Cannot move the compiled program to #{test_result_dir}")
-  system("rm -Rf #{sandbox_dir}/*")
+  call_and_log("Cannot move the compiled program to #{test_result_dir}") {
+    FileUtils.mv("a.out",test_result_dir)
+  }
+  FileUtils.rm_rf("#{sandbox_dir}/.")
 end
 
 require "#{problem_home}/script/test_dsl.rb"
@@ -108,17 +130,29 @@
   $stdout.flush
 
   log "Test number: #{test_num}"
-  execute("cp #{test_result_dir}/a.out #{sandbox_dir}", "Cannot copy the compiled program into #{sandbox_dir}")
+  call_and_log("Cannot copy the compiled program into #{sandbox_dir}") {
+    FileUtils.cp("#{test_result_dir}/a.out", sandbox_dir)
+  }
   begin
     execute("#{problem_home}/script/run #{language} #{test_num}", "Error occured during execution of the run script")
   rescue
     # do nothing
   end
-  execute("mkdir #{test_result_dir}/#{test_num}", "Cannot create directory #{test_result_dir}/#{test_num}")
-  execute("mv #{sandbox_dir}/result #{test_result_dir}/#{test_num}", "Cannot copy the result file into #{test_result_dir}/#{test_num}")
-  execute("mv #{sandbox_dir}/comment #{test_result_dir}/#{test_num}", "Cannot copy the comment file into #{test_result_dir}/#{test_num}")
-  execute("mv #{sandbox_dir}/output.txt #{test_result_dir}/#{test_num}", "Cannot copy the output file into #{test_result_dir}/#{test_num}")
-  execute("rm -Rf #{sandbox_dir}/*", "Cannot clear #{sandbox_dir}")
+  call_and_log("Cannot create directory #{test_result_dir}/#{test_num}") {
+    FileUtils.mkdir "#{test_result_dir}/#{test_num}"
+  }
+  call_and_log("Cannot copy the result file into #{test_result_dir}/#{test_num}") {
+    FileUtils.mv "#{sandbox_dir}/result", "#{test_result_dir}/#{test_num}"
+  }
+  call_and_log("Cannot copy the comment file into #{test_result_dir}/#{test_num}") {
+    FileUtils.mv "#{sandbox_dir}/comment", "#{test_result_dir}/#{test_num}"
+  }
+  call_and_log("Cannot copy the output file into #{test_result_dir}/#{test_num}") {
+    FileUtils.mv "#{sandbox_dir}/output.txt", "#{test_result_dir}/#{test_num}"
+  }
+  call_and_log("Cannot clear #{sandbox_dir}") {
+    FileUtils.rm_rf(Dir.glob("#{sandbox_dir}/*"), :secure => true)
+  }
 end
 
 $stdout.print "[done]\n"
diff --git a/test/engine_spec_helper.rb b/test/engine_spec_helper.rb
--- a/test/engine_spec_helper.rb
+++ b/test/engine_spec_helper.rb
@@ -1,17 +1,18 @@
+require 'fileutils'
+
 module GraderEngineHelperMethods
 
   def clear_sandbox
     config = Grader::Configuration.get_instance
-    clear_cmd = "rm -rf #{config.test_sandbox_dir}/*"
-    system(clear_cmd)
+    FileUtils.rm_rf(Dir.glob("#{config.test_sandbox_dir}/*"), 
+                    :secure => true)
   end
 
   def init_sandbox
     config = Grader::Configuration.get_instance
     clear_sandbox
     FileUtils.mkdir_p config.user_result_dir
-    cp_cmd = "cp -R #{config.test_data_dir}/ev #{config.test_sandbox_dir}"
-    system(cp_cmd)
+    FileUtils.cp_r("#{config.test_data_dir}/ev", "#{config.test_sandbox_dir}")
   end
 
   def create_submission_from_file(id, user, problem,